Substrate for protective film for polarizer

ABSTRACT

A base for polarizing plate protective film, which base is stuck on the surface of a polarizing plate of a liquid crystal display board, comprises a biaxially oriented polyester film having a coating layer on one surface thereof and has such properties that: 
         the surface resistance of said coating layer is not higher than 1×10 11  Ω, the adhesive force (P2) of the acrylic adhesives to the coating layer surface is not more than 3,000 mN/cm, the difference (P1-P2) between the adhesive force (P1) of the rubber adhesives to the coating layer surface and the adhesive force (P2) of the acrylic adhesives is not less than 100 mN/cm, and the film haze is not higher than 2%. Such a polarizing plate protective film base excels in antistatic properties, chemical resistance, scratch resistance, handling quality, transparency, etc.

TECHNICAL FIELD

The present invention relates to a base for polarizing plate protectivefilm. More particularly, it relates to a base for polarizing plateprotective film used for protecting the surface of a polarizing plate ofa liquid crystal display board by sticking it to the polarizing platewith an adhesive or such.

BACKGROUND ART

Usually, a liquid crystal display board is constituted by laminatingpolarizing plates on both sides of a liquid crystal cell having liquidcrystal enveloped between two substrates. And a protective film is stuckon the surface of each polarizing plate in order to prevent scratchingor deposition of dust on the polarizing plate surface during circulationof the product or in the process of assemblage of various types ofdisplay devices such as computers, word processors and TV. Theprotective film, after completing its function of protecting thepolarizing plate, is separated and removed as useless matter. Usually,separation and removal of the protective film is accomplished by amethod in which a rubber type adhesive tape is pressed against theprotective film and pulled up.

Hitherto, polyethylene films, ethylene-vinyl acetate copolymer films andthe like have been used as the said protective film. These protectivefilms, however, have disadvantages in that they must be once separatedbefore the tests and again stuck on the board after the completion ofthe tests because the presence of such a protective film may constitutea hindrance to the tests involving the optical evaluations of displayperformance, hue, contrast, contamination with foreign materials, etc.,of the liquid crystal display board.

In Japanese Patent Application Laid-Open (KOKAI) No. 4-30120, as aprotective film which need not be separated at the time of the testsinvolving optical evaluations, there has been proposed a protective filmhaving an optically isotropic adhesive resin layer laminated on anoptically isotropic base film. This protective film, however, is stillunsatisfactory in respects of chemical resistance, scratch resistance,etc., since a film which has been made by casting and which is almostnon-oriented and has a state close to amorphous, is used as base film.

Also, in order to allow detection of more minute defects in a finerpicture when conducting the tests involving optical evaluations ofdisplay performance, hue, contrast, contamination with foreign matter,et., of a liquid crystal display board with a protective film left stuckon the display board, development of a protective film with highertransparency has been desired.

The present invention has been made in view of the above circumstances,and its object is to provide a base for a high-transparency polarizingplate protective film, which excels in antistatic properties, chemicalresistance, scratch resistance, handling quality, transparency, etc.,consequently can facilitate the tests for detecting minute defects, andalso has specific properties such as capability of preventing adhesionof dusts or adhesives to the liquid crystal display board, and whenseparated and removed as useless matter after performing its role ofprotection of the polarizing plate, separation can be effected withease, and which further has the effects of suppressing separationcharging to preclude the possibility of causing damage to the circuitsconnected to the display board by such separation charging.

DISCLOSURE OF THE INVENTION

As a result of strenuous studies on the subject matter mentioned above,the present inventors found that, by use of a specific film, theabove-said problems can be solved with ease, and the present inventionhas been attained on the basis of this finding.

Thus, in an aspect of the present invention, there is provided a basefor polarizing plate protective film, which base is stuck on the surfaceof a polarizing plate of a liquid crystal display board, comprises abiaxially oriented polyester film having a coating layer on one surfacethereof and has such properties that:

-   -   the surface resistance of said coating layer is not higher than        1×10¹¹ Ω,    -   the adhesive force (P2) of the acrylic adhesives to the coating        layer surface is not more than 3,000 mN/cm,    -   the difference (P1 - P2) between the adhesive force (P1) of the        rubber adhesives to the coating layer surface and the adhesive        force (P2) of the acrylic adhesives is not less than 100 mN/cm,        and    -   the film haze is not higher than 2%.

Hereinafter, the present invention is described in detail.

The base for polarizing plate protective film according to the presentinvention, which is designed to be used by sticking it on the surface ofa polarizing plate of a liquid crystal display board, comprises abiaxially oriented polyester film having a coating layer on one surfacethereof. In a preferred embodiment of the present invention, an adhesivelayer is provided on the other side of the polyester film, and a releasefilm is laminated on the surface of the said adhesive layer. The basefor polarizing plate protective film according to the present inventionis produced generally by passing the steps of forming a coating layer,forming an adhesive layer and laminating a release film successively.

In the present invention, the “biaxially oriented polyester film” is afilm obtained by stretching the sheet melt extruded from the extruderhead according to the so-called extrusion method.

The “polyester” comprising the film of the present invention designatesthe polyesters obtained by polycondensing aromatic dicarboxylic acidsand aliphatic glycols. As aromatic dicarboxylic acids, terephthalic acidand 2,6-naphthalenedicarboxylic acid can be mentioned, and as aliphaticglycols, ethylene glycol, diethylene glycol and1,4-cyclohexanedimethanol can be mentioned. Typical examples of thepolyesters are polyethylene terephthalate (PET) andpolyethylene-2,6-naphthalene dicarboxylate (PEN).

The said polyester may be a copolymer containing a third component. Asthe dicarboxylic acid moiety of the copolymer polyester, isophthalicacid, phthalic acid, terephthalic acid, 2,6-naphthalenedicarboxylicacid, adipic acid, sebacic acid, and oxycarboxylic acids (such asP-oxybenzoic acid) can be mentioned. As the glycol moiety, ethyleneglycol, diethylene glycol, propylene glycol, butanediol,1,4-cyclohexanedimethanol, and neopentyl glycol can be mentioned. Two ormore of these dicarboxylic acids and glycols may be used in combination.

In the present invention, in view of the handling quality of the film,it is preferable to contain the particles in the film under thecondition that it does not impair transparency of the film. As suchparticles, for instance silicon dioxide, calcium carbonate, aluminumoxide, titanium dioxide, kaolin, talc, zeolite, lithium fluoride, bariumsulfate, carbon black, and fine particles of heat-resistant polymerssuch as disclosed in Japanese Patent Publication (KOKOKU) No. 59-5216can be mentioned. Two or more types of these particles may be used incombination. The average size of these particles is usually 0.02 to 2μm, preferably 0.05 to 1.5 μm, more preferably 0.05 to 1 μm. The contentof the particles in the film is usually 0.01 to 2% by weight, preferably0.02 to 1% by weight.

Known methods can be used for containing particles in the film. Forinstance, particles may be added at any stage in the polyester producingprocess. It is particularly preferable to add particles as a slurryformed by dispersing the particles in ethylene glycol or the like, atthe stage of esterification or at a stage after the completion of esterexchange reaction and before the start of polycondenstion reaction, andto proceed the polycondensation reaction. It is also possible to useother methods, for example, a method in which a slurry formed bydispersing particles in ethylene glycol or water and a polyestermaterial are blended by using a vented kneader/extruder, and a method inwhich the dried particles and a polyester material are blended by usinga kneader/extruder.

Production of the film is conducted by a method which comprises meltextruding the material from the extruding head according to a knownextrusion method to form a sheet, and stretching and orienting it in thebiaxial directions, viz. in the machine and transverse directions.

In the extrusion method, a polyester is melt extruded from the extrudinghead and cooled and solidified by cooling rolls to obtain anon-stretched sheet. In this case, in order to improve planarity of thesheet, it is necessary to enhance tight attachment of the sheet to therotary cooling drum, for which an electrostatic pinning method or aliquid coating adhesion method is preferably used.

The method of biaxially stretching and orienting the film is notspecifically defined, but a simultaneous biaxial stretching method,successive biaxial stretching method or the like may be used.

In the simultaneous biaxial stretching method, the said non-stretchedsheet is stretched and oriented in both machine and transversedirections simultaneously with the temperature being controlled atusually 70 to 120° C., preferably 80 to 110° C. The stretch ratio isusually 4 to 50 times, preferably 7 to 35 times, more preferably 10 to20 times the original area. Then the sheet is subjected to a heattreatment at 170 to 250° C. under tension or under a relaxation of notmore than 30% to obtain a stretched and oriented film.

In the successive biaxial stretching method, the said non-stretchedsheet is stretched in one direction by a roll or tenter type stretchingmachine. The stretching temperature is usually 70 to 120° C., preferably80 to 110° C., and the stretching ratio is usually 2.5 to 7 times,preferably 3.0 to 6 times. Then, the sheet is further stretched in thedirection perpendicular to the initial stretching direction. Thestretching temperature is usually 70 to 120° C., preferably 80 to 115°C., and the stretch ratio is usually 3.0 to 7 times, preferably 3.5 to 6times. Then the sheet is further subjected to a heat treatment at 170 to250° C. under tension or under a relaxation of not more than 30% toobtain a stretched and oriented film.

For the said stretching, it is possible to use a method in whichstretching in one direction is conducted in two or more stages. In thiscase, it is preferable to carry out the operation so that the stretchratios in the two directions would finally fall within the above-definedranges. Also, if necessary, additional stretching in the machine and/ortransverse direction may be conducted before or after the heattreatment.

In the present invention, film thickness is not specifically defined,but it is usually in the range of 5 to 150 μm, preferably 10 to 100 μm,more preferably 25 to 75 μm. If film thickness is less than 5 μm, liquidcrystal display board surface protective properties of the film maydeteriorate, and also the film handling quality in the wear-resistantlayer forming step or the adhesive layer forming step tend to get worse.On the other hand, if film thickness exceeds 150 μm, because of a dropof flexibility and a decline of total light transmittance, the filmhandling and working properties as a protective film may be adverselyaffected, and also trouble may arise in the tests involving opticalevaluations of display performance, hue, contrast, contamination withforeign materials, etc., of the liquid crystal display board.

The coating layer constituting the film of the present invention isformed, for instance, by applying a cationic copolymer in a state ofbeing dissolved or dispersed in a solvent such as water, methyl alcohol,ethyl alcohol, isopropyl alcohol or the like, on one surface of abiaxially oriented polyester film, and drying the coat. The coatingoperation is not subject to any specific restrictions, and it is usuallycarried out with a coating machine such as air knife coater, bladecoater, bar coater, gravure coater, curtain coater and roll coater.Coating layer thickness is usually in the range of 0.01 to 0.3 μm,preferably 0.05 to 0.2 μm. If coating layer thickness is less than 0.01μm, the adhesive force of the coating layer with an acrylic adhesivetends to elevate, while if the coating thickness exceeds 0.3 μm, thereis formed a visually observable Moiré fringe in the coating layer, whichmay constitute a hindrance to the tests of the polarizing plate orcrystal liquid display board. In the coating, if necessary, otheradditives such as monomer, resin, crosslinking agent, pigment, etc., maybe properly mixed as far as they give no adverse effect on performanceof the cationic copolymer used.

As the “cationic copolymers” referred to herein, those comprisingcationic monomeric units, hydrophobic monomeric units andorganopolysiloxane units as main components can be exemplified.

The cationic monomeric units usable in the present invention are, forinstance, those containing a quaternary ammonium base in the units.Particularly use of the monomeric units represented by the followingformula (a) can provide more excellent antistatic and antifoulingproperties:

wherein A represents O or NH, R² represents hydrogen or CH₃, R³represents a C₂-C₄ alkylene group or —CH₂CH(OH)CH₂—, R⁴, R⁵ and R⁶represent independently a C₁-C₁₀ alkyl or aralkyl group, and Xrepresents a halogen or an alkylsulfate acid ion.

More specifically, the said cationic monomeric units include, forexample, (meth)acrylic monomeric units such as(meth)acryloyloxytrimethylammonium chloride,(meth)acryloyloxyhydroxypropyltrimethyl-ammonium chloride,(meth)acryloyloxytriethylammonium chloride,(meth)acryloyloxydimethylbenzylammonium chloride,(meth)acryloyloxytrimethylammonium chloride, and(meth)acryloyloxytrimethylammoiummethyl sulfate, and (meth)acrylamidetype cationic monomeric units such as(meth)acrylamidopropyltrimethylammonium chloride,(meth)acrylamidopropyltrimethylammonium chloride, and(meth)acrylamidopropyldimethylbenzylammonium chloride.

In these monomeric units, the corresponding monomers may be polymerized,or first their precursors, viz. the monomers containing a ternary aminogroup, such as dimethylaminoethyl(meth)acrylate ordimethylaminopropylacrylamide may be polymerized and then cationizedwith a modifier such as methyl chloride.

The content of the cationic monomeric units in the copolymer ispreferably 15 to 60% by weight. If the content of these monomeric unitsis less than 15% by weight, antistatic properties of the product tendsto prove unsatisfactory. If their content exceeds 60% by weight,blocking tends to occur.

The hydrophobic monomeric units usable in the present invention includevarious types of monomeric materials, for example, alkyl(meth)acrylatessuch as methyl(meth)acrylate, ethyl(meth)acrylate, butyl(meth)acrylate,isobutyl(meth)acrylate, tertiary-butyl(meth)acrylate,cyclohexyl(meth)acrylate, 2-ethylhexyl(meth)acrylate,lauryl(meth)acrylate, tridecylacrylate and stearyl(meth)acrylate,styrene, and vinyl esters such as vinyl acetate.

The content of the hydrophobic monomeric units in the copolymer ispreferably 30 to 84.9% by weight. If their content is less than 30% byweight, antifouling properties of the product tend to becomeunsatisfactory, and if their content exceeds 84.9% by weight, antistaticperformance tends to lower relatively.

The organopolysiloxane units usable in the present invention arepreferably those represented by the following formula (b):

wherein R¹ and R^(1′) represent independently a C₁-C₁₀ alkyl or phenylgroup, and n is an integer of 5 or more.

If n in the above formula (b) is less than 5, it may become difficult toafford sufficient lubricity to the. obtained copolymer.

The ratio of the organopolysiloxane units contained in the cationiccopolymer is usually 0.1 to 20% by weight. If such a ratio is less than0.1% by weight, antifouling properties tend to become unsatisfactory.Also, antifouling properties are not bettered additionally even if theabove ratio exceeds 20% by weight.

Specifically, the organopolysiloxane units in the cationic copolymer arepreferably incorporated in the copolymer by using their precursorsrepresented by the following formula (c), (d) or (e). The precursorsrepresented by the following formulae can be incorporated in thecopolymer by using a reactive group D.

In the above formulae (c) to (e), D represents a radical polymerizablegroup selected from the group consisting of vinyl groups,acryloyloxyalkyl groups and methacryloyloxyalkyl groups, an epoxy groupsuch as glycidoxyalkyl group, an aminoalkyl group or a mercaptoalkylgroup; R represents a C₁-C₁₀ alkyl or phenyl group; m is an integer of 1to 20; and n is an integer of 5 or more.

As the precursor, it is possible to use those commercially available asreactive silicone, but in view of the fact that reactivity lowers whenthe molecular weight increases, it is preferable to use ones in which nin their formulae is not more than 200 in case where the precursor is(c) or (d) and not more than 400 even in case where the reactive groupsof the formula (e) are present in large number.

As for the method of incorporating these precursors as a cationiccopolymer component, in case where the reactive group D is apolymerizable group, the precursor is polymerized simultaneously withother monomers, and in case where D is a mercaptoalkyl group, a cationicmonomer (a) and a hydrophobic monomer (b) are polymerized in thepresence of the said precursor, whereby the precursor can be introducedefficiently by chain transfer. Further, in case where the reactive groupD is an epoxy group, copolymerization of a cationic monomer (a) and ahydrophobic monomer (b) is carried out together with other monomers, forexample, hydrochlorides of carboxyl group-containing monomers such as(meth)acrylic acid having reactivity with epoxy groups or tertiary aminegroup-containing monomers such as dimethylaminoethyl (meth)acrylate, andthe resulting product is reacted with the epoxy group of the precursor.

Likewise, in case where the reactive group D is an aminoalkyl group,copolymerization of a cationic monomer (a) and a hydrophobic monomer (b)is carried out together with a monomer reactive with amino groups, suchas glycidyl (meth)acrylate, and the resulting product is further reactedwith the amino group of the precursor. If necessary, other hydrophilicmonomers such as hydroxyethyl (meth)acrylate and vinylpyrrolidone may becontained as a copolymer component provided that they produce no adverseeffect on antistatic and antifouling properties of the product.

As the polymerization method, known radical polymerization methods suchas bulk polymerization, solution polymerization and emulsionpolymerization can be used. The preferred polymerization method issolution polymerization in which the respective monomers are dissolvedin a solvent, and after adding a polymerization initiator, the mixtureis heated and stirred in a stream of nitrogen. As the solvent, water andalcohols such as methyl alcohol, ethyl alcohol and isopropyl alcohol arepreferred, and these solvents may be used in admixture. As thepolymerization initiator, peroxides such as benzoyl peroxide and lauroylperoxide and azo compounds such as azobisbutyronitrile andazobisvaleronitrile are preferably used. The monomer concentration isusually 10 to 60% by weight, and the polymerization initiator is usually0.1 to 10% by weight based on the monomers.

The molecular weight of the cationic copolymer can be set at any levelaccording to the polymerization conditions such as polymerizationtemperature, type and amount of the polymerization initiator used,amount of the solvent used and chain transfer, type of theorganopolysiloxane precursor used, content of the reactive groups, etc.Generally, the molecular weight of the obtained cationic copolymer ispreferably in the range of 5,000 to 500,000. The coating layer formed onthe biaxially oriented polyester film by using the coating materialprepared in the manner described above is excellent in anti-stickquality, etc.

Other cationic copolymers usable in the present invention are, forinstance, those comprising as main components a polymer havingorganopolysiloxane units and quaternary ammonium salt units, and anactive energy ray-curing resin containing a polyfunctional acrylatehaving three or more acryloyl groups in the molecule.

The polymers having organopolysiloxane units and quaternary ammoniumsalt units may be ones having (meth)acryloyl groups in the side chain asrequired. These polymers having organopolysiloxane units and quaternaryammonium salt units can be obtained by polymerizing anorganopolysiloxane compound having one radical polymerizable group in amolecule or two mercapto groups in a molecule and a tertiary aminecompound having one radical polymerizable F group in a molecule, andconverting the obtained tertiary amine polymeric compound to aquaternary ammonium salt with a quaternarizing agent.

When copolymerizing an organopolysiloxane compound and a tertiary aminecompound having one radical group in a molecule, other (meth)acrylicesters may be copolymerized in addition to these monomers. The polymershaving organopolysiloxane units and quaternary ammonium salt units canbe also obtained by polymerizing an organopolysiloxane compound havingone radical polymerizable group in a molecule or two mercapto groups ina molecule and a quaternary ammonium salt having one radicalpolymerizable group in a molecule. When copolymerizing anorganopolysiloxane compound and a quaternary ammonium salt having oneradical polymerizable group in a molecule, other (meth)acrylic estersmay be copolymerized in addition to these monomers.

The organopolysiloxane compounds having one radical polymerizable groupin a molecule are not specifically defined as far as they have oneradical polymerizable group such as acryl, methacryl, styryl, cinnamicester, vinyl and ally in a molecule, but in view of the ease ofcopolymerization of an organopolysiloxane compound having one radicalpolymerizable group in a molecule and a tertiray amine compound having aradical polymerizable group or quaternary ammonium salt having a radicalpolymerizable group, they are preferably those organopolysiloxanecompounds which have an acrylic, methacrylic or styrylic radicalpolymerizable group.

Also, when polymerizing a tertiary amine compound having a radicalpolymerizable group or a quaternary ammonium salt having a radicalpolymerizable group, the organopolysiloxane compounds having twomercapto groups in a molecule which have been introduced into thepolymer through sulfide linkage by chain transfer can be preferablyused. The orgaonopolysiloxane units contained in theseorganopolysiloxane compounds are represented by the following formula(f):

wherein R⁷ and R^(7′) represent independently a methyl or phenyl group,and n is an integer of 5 or more.

The number-average molecular weight of the organopolysiloxane compoundshaving one radical polymerizable group in a molecule is usually 400 to60,000, preferably 1,000 to 30,000.

The tertiary amine compounds having one radical polymerizable group in amolecule are represented by the following formula (g):

wherein R⁹ represents H or CH₃, R⁸ and R^(8′) represent independently Hor a C₁-C₉ alkyl group which may contain a substituent group, and k isan integer of 1 to 6.

As such tertiary amine compounds having a radical polymerizable group,for example, N,N-dimethylaminoethyl(meth)acrylate,N,N-diethylaminoethyl(meth)acrylate, N,N-dimethylaminopropylmethacrylate, N,N-dimethylaminobutyl methacrylate,N,N-dihydroxyethylaminoethyl methacrylate, N,N-dipropylaminoethylmethacrylate, and N,N-dibutylaminoethyl methacrylate can be mentioned.

As the quaternary ammonium salts having one radical polymerizable groupin a molecule, for example, those obtained by quaternarizing tertiaryamine compounds represented by the above-shown formula (d) with aquaternarizing agent, for example, alkyl chlorides such as methylchloride and butyl chloride, halides such as methyl bromide,methylbenzyl chloride and benzyl chloride, alkyl sulfates such asdimethyl sulfate, diethyl sulfate and dipropyl sulfate, and sulfonicesters such as methyl p-toluenesulfonate and methyl benzenesulfonate canbe mentioned.

In the copolymerization of an organopolysiloxane compound having oneradical polymerizable group or two mercapto groups in a molecule and atertiary amine compound or quaternary ammonium salt having one radicalpolymerizable group in a molecule, it is possible to use (meth)acrylicesters in addition to the said monomers.

As such (meth)acrylic esters, for example, methyl(meth)acrylate,ethyl(meth)acrylate, n-butyl(meth)acrylate, isobutyl(meth)acrylate,2-ethylhexyl(meth)acrylate, benzyl(meth)acrylate,cyclohexyl(meth)acrylate, isobonyl(meth)acrylate,dicyclopentenyl(meth)acrylate, dicyclopentenyloxyethyl(meth)acrylate,ethoxyethyl(meth)acrylate, ethylcarbitol(meth)acrylate,butoxyethyl(meth)acrylate, cyanoethyl(meth)acrylate,glycidyl(meth)acrylate, 2-hydroxyethyl(meth)acrylate and2-hydroxypropyl(meth)acrylate, which have one radical polymerizablegroup in a molecule, can be mentioned.

In the copolymerization of an organopolysiloxane compound having oneradical polymerizable group or two mercapto groups in a molecule and atertiary amine compound or quaternary ammonium salt having one radicalpolymerizable group in a molecule, the amount of the organopolysiloxanecompound having one radical polymerizable group or two mercapto groupsin a molecule, which is used for the copolymerization, is usually 1 to40% by weight, preferably 5 to 30% by weight, in 100% by weight of thecopolymerizable monomeric mixture. If this amount is less than 1% byweight, it may prove unable to sufficiently bleed out the vinyl polymerto the coating layer surface, and the desired antistatic properties maynot be afforded to the coating layer. If the said amount exceeds 40% byweight, no satisfactory antistatic properties may be obtained because ofthe drop of the ratio of the tertiary amine compound or quaternaryammonium salt having one radical polymerizable group in a molecule.

On the other hand, the amount of the tertiary amine compound orquaternary ammonium salt having one radical polymerizable group in amolecule is usually 60 to 99% by weight, preferably 60 to 95% by weightin 100% by weight of the copolymerizable monomers. If this amount isless than 60% by weight, satisfactory antistatic properties may not beprovided to the coating layer. If the said amount exceeds 99% by weight,there may also not be provided desired antistatic properties to thecoating layer because of the drop of the ratio of the organopolysiloxanecompound.

The copolymerization of the said monomers, viz. an organopolysiloxanecompound, a tertiary amine compound having a radical polymerizablegroup, a (meth)acrylic ester and a quaternary ammonium salt having aradical polymerizable group is usually carried out in a solvent using aradical polymerization initiator. As the solvent, there can be mentionedalcohols such as methyl alcohol, ethyl alcohol, n-propyl alcohol,iso-propyl alcohol and n-butyl alcohol, ketones such as acetone,methylethyl ketone, methylisobutyl ketone and cyclohexanone, esters suchas ethyl acetate, propyl acetate and butyl acetate, aromatichydrocarbons such as toluene and xylene, ethers such as2-methoxyethanol, 2-ethoxyethanol, 2-butoxyethanol, ethylene glycoldimethyl ether, ethylene glycol diethyl ether and diethylene glycoldimethyl ether, ether-esters such as 2-methoxyethyl acetate,2-ethoxyethyl acetate and 2-butoxyethyl acetate, and water. Thesesolvents may be used in admixture.

As the radical polymerization initiator used for the polymerizationreaction, organic peroxides such as benzoyl peroxide, di-t-butylperoxide and cumene hydroperoxide, and azo compounds such as2,2′-azobisisobutyronitrile, 2,2′-azobis(2,4-dimethylvaleronitrile) and2,2′-azobis(4-methoxy-2,4-dimethylvaleronitrile) are used favorably. Themonomer concentration in the polymer solution is usually 10 to 60% byweight, and the polymerization initiator is used in an amount of usually0.1 to 10% by weight, preferably 0.3 to 5% by weight based on themonomeric mixture.

In case of copolymerizing an organopolysiloxane compound, a tertiaryamine compound having one radical polymerizable group in a molecule and,if necessary, a (meth)acrylic ester, the tertiary amine polymer compoundobtained from the copolymerization is converted to a quaternary ammoniumsalt by using a quaternarizing agent. As the quaternarizing agent, forexample, alkyl chlorides such as methyl chloride and butyl chloride,halides such as methyl bromide, methylbenzyl chloride and benzylchloride, alkyl sulfates such as dimethyl sulfate, diethyl sulfate anddipropyl sulfate, and sulfonic esters such as methyl p-toluenesulfonateand methyl benzenesulfonate can be mentioned.

Among the polymers having organopolysiloxane units and quaternaryammonium salt units obtained by these methods, those prepared byconverting the tertiary amine polymer compound obtained bycopolymerizing an orpanopolysiloxane compound having one radicalpolymerizable group or two mercapto groups in a molecule, a tertiaryamine compound having one radical polymerizable group in a molecule and,if necessary, an (meth)acrylic ester, to a quaternary ammonium salt withan alkyl chloride, are especially preferred brcause they have excellentcompatibility with the polyfunctional acrylates having three or moreacryloyl groups in the molecule, and are also capable of providing acoating layer with good transparency.

When a polymer having organopolysiloxane units having (meth)acryloylgroups in the side chain and quaternary ammonium salt units is used asthe polymer having organopolysiloxane units and quaternary ammonium saltunits, linkage is formed between this polymer and the polyfunctionalacrylate upon irradiation with the active energy rays to provide animprovement of durability of antistatic performance.

Among the polymers having organopolysiloxane units and quaternaryammonium salt units, those having (meth)acryloyl groups in the sidechain can be obtained, for instance, by additionally copolymerizingglycidyl (meth)acrylate when copolymerizing an organopolysiloxanecompound and a tertiary amine compound or quaternary ammonium salthaving one radical polymerizable group in a molecule, and then adding a(meth)acrylic acid (in case of using a tertiary amine compound, theobtained tertiary amine polymer compound is further converted to aquaternary ammonium salt with a quaternarizing agent).

These polymers can be also obtained by adding an 1:1 (by mole) adduct ofa (meth)acrylate having hydroxyl groups such as hydroxyethyl(meth)acrylate and hydroxypropyl (meth)acrylate and an isocyanatecompound such as tolylene diisocyanate, isophorone diisocyante andhexamethylene diisocyanate after additionally copolymerizing a(meth)acrylate having hydroxyl groups such as hydroxyethyl(meth)acrylate, hydroxypropyl (meth)acrylate, pentaerythritoltriacrylate or dipentaerythritol pentaacrylate when copolymerizing anorganopolysiloxane compound and a tertiary amine compound or quaternaryammonium salt having one radical polymerizable group in a molecule (incase of using a tertiary amine compound, the obtained tertiary aminepolymer compound is further converted to a quaternary ammonium salt witha quaternarizing agent).

Among the polymers having organopolysiloxane units and quaternaryammonium salt units and having (meth)acryloyl groups in the side chainobtained by these methods, those obtained by copolymerizing anorganopolysiloxane compound having one radical polymerizable group ortwo mercapto groups in a molecule, a tertiary amine compound having oneradical polymerizable group in a molecule and a (meth)acrylic esterhaving functional groups, then adding to the resulting polymer acompound having (meth)acryloyl groups, and converting the tertiary aminecompound to a quaternary ammonium salt with an alkyl chloride areespecially preferred as they show excellent compatibility with thepolyfunctional acrylates having three or more acryloyl groups in themolecule and are also capable of provide a coating layer with goodtransparency.

As the polyfunctional acrylates having three or more acryloyl groups inthe molecule, for example, trimethylolpropane triacrylate, ethyleneoxide-modified trimethylolpropane triacrylate, propylene oxide-modifiedtrimethylolpropane triacrylate, tris(acryloxyethyl)isocyanurate,caprolactone-modified tris(acryloxyethyl)isocyanurate, pentaerythritoltriacrylate, pentaerythritol tetraacrylate, dipentaerythritoltetraacrylate, dipentaerythritol pentaacrylate, dipentaerythritolhexacrylate, alkyl-modified dipentaerythritol triacrylate,alkyl-modified dipentaerythritol tetraacrylate, alkyl-modifieddipentaerythritol pentaacrylate, captrolactone-modifieddipentaerythritol hexaacrylate, carboxyl group-containing polyfunctionalacrylates obtained by reacting tetracarboxylic acid dianhydrides andhydroxyl group-containing polyfunctional acrylates having a hydroxylgroup and three or more acryloyl groups in the molecule, and mixtures oftwo or more of these acrylates can be mentioned.

As the concrete examples of the tetracarboxylic acid dianhydrides,pyromellitic acid dianhydride, 3,3′,4,4′-benzophenonetetracarboxylicacid dianhydride, 4,4′-biphthalic acid anhydride, 4,4′-oxodiphthalicacid anhydride, 4,4′-(hexafluoroisopropylidene)diphthalic acidanhydride, 1,2,3,4-cyclopentatetracarboxylic acid dianhydride,5-(2,5-dioxotetrahydrofur)-3-methyl-3-cyclohexene-1,2-dicarboxylic acidanhydride, 4-(2,5-dioxotetrahydrofuran-3-il)-tetralin-1,2-dicarboxylicacid anhydride, 3,4,9,10-perillenetetracarboxylic acid dianhydride, andbicyclo[2.2.2]octo-7-en-2,3,5,6-tetracarboxylic acid dianhydride can bementioned.

As the concrete examples of the hydroxyl group-containing polyfunctionalacrylates having a hydroxyl group and three or more acryloyl groups inthe molecule, pentaerythritol triacrylate, dipentaerythritoltetraacrylate, dipentaerythritol pentaacrylate and mixtures thereof canbe mentioned. Among these polyfunctional acrylates having three or moreacryloyl groups in the molecule, dipentaerythritol hexaacrylate,dipentaerythritol pentaacrylate, carboxyl group-containingpolyfunctional acrylates obtained by reacting tetracarboxylic aciddianhydrides and hydroxyl group-containing polyfunctional acrylateshaving a hydroxyl group and three or more acryloyl groups in themolecule, and mixtures thereof are especially preferred as they canprovide a coating layer with excellent abrasion resistance.

In addition to the polymers having organopolysiloxane units andquaternary ammonium salt units and the polyfunctional acrylates havingthree or more acryloyl groups in the molecule, it is possible to useother polymeric monomers such as arylates having one or two acryloylgroups in the molecule. Specifically, it is possible to use urethaneacrylates or epoxy acrylates having two acryloyl groups within limitsnot deteriorating abrasion resistance and antistatic properties (forexample, not more than 20% by weight in the components of coatinglayer).

In case of using ultraviolet rays as the active energy rays for curingof the coating composition, a photopolymerization initiator is used inaddition to a polymer having organopolysiloxane units and quaternaryammonium salt units and a polyfunctional acrylate having three or moreacryloyl groups in the molecule such as mentioned above.

As the photopolymerization initiator, for example,2,2-ethoxyacetophenone, 1-hydroxycyclohexylphenyl ketone, dibenzoyl,benzoin, benzoinmethyl ether, benzoinethyl ether, benzoinisopropylether, p-chlorobenzophenone, p-methoxybenzophenone, Michler's ketone,acetophenone, 2-chlorothioxanetone, anthraquinone, phenyl disulfide,2-methyl-[4-(methylthio)phenyl]-2-morpholinopropane-1-one,2-hydroxy-2-methyl-1-phenyl-propane-1-one, and2,4,6-trimethylbenzoyl-diphenyl-phsophine oxide can be mentioned. Thesephotopolymerization initiators can be used alone or as a mixture of twoor more.

As the photopolymerization initiator assistant, tertiary amines such astriethylamine, triethanolamine and 2-dimethylaminoethanol,alkylphosphines such as triphenylphosphine, and thioethers such asβ-thiodiglycol can be mentioned.

As the modifying agents, coating properties improver, defoaming agent,thickener, inorganic particles, organic particles, lubricant, organicpolymers, dyes, pigment, stabilizing agent, etc., can be mentioned.These modifying agents are used within limits not impairing thereactions induced by the active energy rays and their use can improvethe properties of the active energy ray-curing resin layer according tothe purpose of use of the product film. In the composition of the activeenergy ray-curing resin layer, the solvent used in forming the copolymermay be blended for the adjustment of viscosity, improvement of coatingworkability and control of coating thickness.

In the active energy ray-curing coating composition of the presentinvention, various additives such as ultraviolet absorber (e.g.benzotriazole-based, benzophenone-based, salicylic acid-based andcyanoacrylate-based ultraviolet absorbers), ultraviolet stabilizer (e.g.hindered amine-based ultraviolet stabilizer), antioxidant (e.g.phenolic, sulfuric and phosphoric antioxidants), anti-blocking agent,slip agent and leveling agent may be blended for the purpose ofimproving the coating layer properties.

In the present invention, the content of the polymer havingorganopolysiloxane units and quaternary ammonium salt units in theactive energy ray-curing coating composition is usually 1 to 40% byweight, preferably 5 to 25% by weight in 100% by weight of the solids.If this content is less than 1% by weight, there may not be obtained acoating layer having satisfactory antistatic properties. Also, if thecontent exceeds 40% by weight, abrasion resistance of the coating layertend to lower.

In the present invention, the content of the polyfunctional acrylatehaving three or more acryloyl groups in the active energy ray-curingcoating composition is usually 60 to 99% by weight, preferably 75 to 95%by weight in 100% by weight of the solids. If this content is less than60% by weight, there may not be obtained a coating layer havingsatisfactory abrasion resistance, and if that content exceeds 99% byweight, a coating layer with satisfactory antistatic properties may notbe obtained.

In the present invention, the solids concentration of the active energyray-curing coating composition is not specifically defined, but it isusually adjusted to be 0.5 to 20% by weight, preferably 1 to 10% byweight, more preferably 1 to 5% by weight.

In the present invention, the content of the photopolymerizationinitiator in the activation energy ray-curing coating composition is notspecifically defined provided that it is sufficient to cause curing ofthe resin composition, but it is usually 0.5 to 20% by weight,preferably 1 to 10% by weight, more preferably 1 to 5% by weight in 100%by weight of the solids.

In the present invention, formation of the coating layer is accomplishedby a method in which the coating composition is applied on one side ofthe film and cured. As the coating method, reverse roll coating, gravureroll coating, rod coating, air knife coating, etc, can be used.

Curing of the applied coating composition is performed by the activeenergy rays or heat. As the active energy rays, ultraviolet rays,visible light rays, electron rays, x-rays, α-rays, β-rays, γ-rays, etc.,can be used. As the heat source, infrared heater, heating oven, etc.,can be used. Irradiation with the active energy rays is usuallyconducted from the coating layer side, but it may be conducted from theopposite side of the coating layer for enhancing adhesion to the film.If necessary, a reflector which is capable of reflecting the activeenergy rays may be utilized. The coating film cured by the active energyrays excels particularly in scratch resistance.

In the film of the present invention, it is essential that surfaceresistance of the coating layer is not more than 1×10¹¹ Ω. When surfaceresistance of the coating layer exceeds the above value, staticelectricity tends to be generated to encourage deposition of dust.Surface resistance of the coating layer is preferably not more than5×10¹⁰ Ω, more preferably not more than 1×10¹⁰ Ω. In the presentinvention, the lower threshold value of surface resistance for retainingantistatic properties is 1×10⁷ Ω. If surface resistance is less than1×10⁷ Ω, the surface shows conductivity, so that when the protectivefilm is separated, the electrons which caused separation charging becomeconductive, which may result in breaking down circuits of the liquidcrystal display board.

In the present invention, adhesive force (P2) of the acrylic adhesivesto the coating layer surface is not more than 3,000 mN/cm, preferablynot more than 2,750 mN/cm, more preferably not more than 2,500 mN/cm.The protective film base according to the present invention is stored ina stacked up state, so that in the step of cutting it to a desired sizefor storage, the adhesive layer which was accidentally squeezed out frombetween the polyester film and the release film may come into contactwith the coating layer of another protective film. Such contact of theadhesive layer with the coating layer is undesirable as it becomes acause of adhesion of the adhesive to the coating layer and its foulingwhen the adhesive force of the adhesive exceeds 3,000 mN/cm.

In the present invention, the difference (P1-P2) between adhesive force(P1) of rubber adhesives to the coating layer surface and adhesive force(P2) of acrylic adhesives is not less than 100 mN/cm, preferably notless than 200 mN/cm. If the difference in adhesive force is less than100 mN/cm, separation of the protective film is difficult when it istried to separate the film by using a rubber adhesive tape in the finalstep.

In the film of the present invention, film haze is not more than 2%,preferably not more than 1.5%. When film haze exceeds 2%, it becomesdifficult to detect finer defects when the tests involving opticalevaluations of display performance, hue, contract, contamination withforeign materials, etc., of the liquid crystal display board areconducted with the protective film left stuck on the board.

A preferred embodiment of the present invention is a laminated filmcomprising a biaxially oriented polyester film having a coating layer onone surface thereof and having laminated on the other side an adhesivelayer and a release film for protecting it.

In the present invention, the adhesive layer comprises a known adhesive,for example, acrylic adhesive, rubber adhesive, block copolymericadhesive, polyisobutylene adhesive and silicone adhesive. Generally,these adhesives are offered as a composition with an elastomer,tackifier, softener (plasticizer), deterioration preventive agent,filler, crosslinking agent, etc.

As the elastomer, for example, natural rubber, synthetic isoprenerubber, reclaimed rubber, SBR, block copolymer, polyisobutyrene, butylrubber, polyacrylic ester copolymer and silicone rubber can bementioned, of which appropriate one is selected according to the type ofthe adhesive to be applied.

As the tackifier, for example, rosin, hydrogenated rosin esters, terpeneresin, aromatic modified terpene resin, hydrogenated terpene resin,terpene phenol resin, aliphatic petroleum resin, aromatic petroleumresin, alicyclic hydrogenated petroleum resin, cumarone-indene resin,styrene resin, alkyl phenol resin and xylene resin can be mentioned.

As the softener, for example, paraffinic process oil, naphthenic processoil, aromatic process oil, liquid polybutene, liquid polyisobutyrene,liquid polyisoprene, dioctyl phthalate, dibutyl phthalate, castor oiland tall oil can be mentioned.

As the deterioration preventive agent, for example, aromatic aminederivatives, phenol derivatives and organothio acid salts can bementioned.

As the filler, for example, zinc white, titanium white, calciumcarbonate, clay, pigment and carbon black can be mentioned. In casewhere a filler is contained, it is used within limits not greatlyaffecting the total light transmittance of the protective film.

As the crosslinking agent, for example, sulfur, a curing assistant and acuring accelerator (representative example: zinc dibutylthiocarbamate)are used for crosslinking of natural rubber adhesives. Polyisocyanatesare used as the crosslinking agent which is capable of crosslinking theadhesives made of natural rubber and carboxylic acid copolymerpolyisoprene at room temperature. Polyalkylphenol resins are used as acrosslinking agent having characteristically heat resistance andnon-staining properties for crosslinking of butyl rubber and naturalrubber. The organic peroxides such as benzoyl peroxide and dicumylperoxide are available for crosslinking of the adhesives made ofbutadiene rubber, styrene rubber and natural rubber, and use of suchorganic peroxides provides non-staining adhesives. Polyfunctionalmethacrylic esters are used as crosslinking assistant. There are alsoknown adhesives formed by other types of crosslinking such asultraviolet crosslkinkg and electron ray crosslinking.

Formation of the adhesive layer, although not specifically defined, isconducted by a method in which an adhesive is applied on the othersurface of the base film. As the coating method, the same method as usedfor forming the abrasion-resistant layer can be used. Thickness of theadhesive layer is usually in the range of 0.5 to 100 μm, preferably 1 to50 μm.

In the present invention, the adhesive force of the adhesive layer isadjusted so that when an adhesive tape was pressed against the coatinglayer and pulled up, the adhesive layer will be separated away from thesurface of the polarizing plate together with the biaxially orientedpolyester film. In this case, the adhesive force between the polarizingplate and the adhesive layer is preferably adjusted to stay within therange of 10 to 400 mN/cm. On the surface of the adhesive layer islaminated a known release film for the convenience of handling. Thepolarizing plate referred to herein is of a structure in which aprotective film such as triacetate cellulose film is laminated on bothsides of a polarizing film made by containing iodine, dichromic dye,etc., in polyvinyl alcohol and monoaxially orienting the obtained film.

The total light transmittance (TL) of the polarizing plate protectivefilm base of the present invention having the above-described structureis not specifically defined, but it is usually not less than 80%,preferably not less than 85%. Consequently, the tests involving opticalevaluations of display performance, hue, contrast, contamination withforeign materials, etc., of the liquid crystal display board can becarried out with the protective film kept stuck on the surface of thepolarizing plate.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the present invention is described in further detail withreference to the examples thereof, but the present invention is notlimited to these examples but can be embodied in other forms as wellwithout departing from the scope of the invention. In the followingExamples and Comparative Examples, all “parts” are by weight unlessotherwise noted. Also, the determination methods and evaluationstandards used in the present invention are as explained below.

(1) Surface Resistance (9) of the Coating Layer

Using “Hiresta-UP MCP-HT 450” mfd. by Dia Instruments Co., Ltd., thespecimen was set in an atmosphere of 23° C. and 50% RH, an electricvoltage of 500 V was applied thereto, and surface resistance (Ω) afterone-minute charging (voltage application time: 1 min.) was measured. Theelectrode type used here was a concentric circular electrode assemblywith the outer diameter of the main electrode being 50 mm and the innerdiameter of the opposite electrode being 53.2 mm.

(2) Peel Force (P2) of the Coating Layer Against Acrylic Adhesive

A double-sided adhesive tape (“No. 502” mfd. by Nitto Denko Corporationwas affixed on the coating layer and press bonded thereto by a rubberroller under a linear pressure of 450 g/cm, and the laminate was cutinto a 50 mm wide piece to prepare a specimen for measuring peel force.After allowed to stand for one hour after press bonding, the tape waspeeled at a pulling rate of 300 mm/min in the direction of 180 degreesby using an Instron tensile tester, and the mean value of the stressproduced thereby was expressed as peel force of the specimen. This testwas repeated 10 times, and the arithmetic mean of 10 measurements waspresented here as peel force. The atmosphere under which this test wasconducted was a standard state of 23° C. and 50% RH. (3) Peel force (P2)of the coating layer by rubber adhesives

Cellotape (registered trade name) made by Nichiban Co., Ltd. was affixedon the coating layer and press bonded by a rubber roller under a linearpressure of 450 g/cm to prepare a specimen for measuring peel force.After allowed to stand for one hour after press bonding, the tape waspeeled at a pulling rate of 300 mm/min in the direction of 180 degreesby using an Instron tensile tester, and the mean value of the stressproduced thereby was expressed as peel force of the specimen. This testwas repeated 10 times and the arithmetic mean of 10 measurements waspresented here as peel force. The atmosphere under which this test wasconducted was a standard state of 23° C. and 50% RH.

(4) Presence or Absence of Adhesion of Dusts

Cigarette ash was dropped onto the surface of the coating layer, andafter letting it make a turn (360-degree turn), the condition ofadhesion of ash was observed, thereby assessing the presence or absenceof adhesion of dusts.

(5) Presence or Absence of Adhesion of the Adhesive

An acrylic adhesive was rubbed on the surface of the coating layer, andthe presence or absence of adhesion of the adhesive on the layer surfacewhen it was tried to rub off the adhesive with fingers was assessed.

(6) Coating Layer Thickness

A small piece of coated film was stationary-molded with an epoxy resinand cut by a microtome, and a section of the film was observed through atransmission electron microscope. In that section, the coating layer canbe observed by light and darkness substantially parallel to the filmsurface. The distance of the coating layer was averaged for eachtransmission electron microphotograph to calculate thickness. Thisoperation was conducted on at least 50 copies of photograph. 10measurements from both largest and smallest measurements of thicknesswere crossed out, and the arithmetic mean of the remaining 30measurements was presented as thickness of the coating layer.

(7) Total Light Transmittance

Total light transmittance of the laminated film having a coating layerprovided on one surface of a biaxially oriented polyester film wasmeasured by an integrating sphere type turbidimeter NDH-300A mfd. byNippon Denshoku Industries CO., Ltd.

(8) Haze

Haze of the laminated film having a coating layer provided on onesurface of a biaxially oriented polyester film was measured by anintegrating sphere type turbidimeter NDH-300A mfd. by Nippon DenshokuIndustries Co., Ltd.

(9) Clarity

Sample films were placed 2 mm apart from each other on the GradationColor Scale [1] in the Laser Dot Color Chart made by GE Kikaku CenterInc. and clarity was judged visually and ranked as follows.

-   -   A: Visible as clearly as the original throughout.    -   B. Hard to see up to the position of 5% half-tone dot density.    -   C: Hard to see up to the position of 10% half-tone dot density.    -   D: Hard to see up to the position of 20% half-tone dot density.

In the above ranking, A and B are of the levels that present nopractical problem.

PRODUCTION EXAMPLE 1 (POLYESTER A)

100 parts of dimethyl terephthalate, 60 parts of ethylene glycol and0.09 parts of magnesium acetate tetrahydrate were supplied into areactor. The mixture was heated to distill away methanol and carry outan ester exchange reaction, the temperature being raised to 230° C.taking 4 hours after start of the reaction to substantially complete theester exchange reaction. Then an ethylene glycol slurry containing 0.03parts of silica particles having an average size of 1.54 μm was added tothe reaction system, after which 0.04 parts of ethyl acid phosphate and0.01 part of germanium oxide were further added, with the temperaturebeing raised to reach 280° C. while the pressure lowered to reach 15mmHg in 100 minutes. The pressure was kept on reducing gradually tofinally reach 0.3 mmHg. 4 hours thereafter, the system was returned tonormal pressure, obtaining polyester A. The content of silica particlesin polyester A was 0.03% by weight.

PRODUCTION EXAMPLE 2 (POLYESTER B)

The same procedure as defined in Production Example 1 was conductedexcept that while an ethylene glycol slurry containing 0.03 parts ofsilica particles having an average size of 1.54 μm was added to thereaction system in Production Example 1, an ethylene glycol slurrycontaining 0.1 part of silica particles having an average size of 1.54μm was added to the reaction system in this example to obtain polyesterB. The content of silica particles in polyester B was 0.1% by weight.

PRODUCTION EXAMPLE 3 (POLYESTER FILM A1)

Polyester A was dried in an inert gas atmosphere at 180° C. for 4 hours,then melt extruded by a melt extruder at 290° C. and cooled andsolidified on a cooling roll set at a surface temperature of 40° C. byusing the electrostatic pinning method to obtain a non-stretched sheet.The obtained sheet was stretched 3.5 times in the machine direction at85° C., then stretched 3.7 times transversely at 100° C. and furtherheat set at 230° C. to obtain polyester film A1 with a thickness of 38μm.

PRODUCTION EXAMPLE 4 (POLYESTER FILM B)

The same procedure as defined in Production Example 3 was conductedexcept that polyester A was replaced by polyester B to obtain 38 μmthick polyester film B1.

PRODUCTION EXAMPLE 5 (POLYESTER C)

The same procedure as defined in Production Example 1 was conductedexcept that while an ethylene glycol slurry containing 0.03 parts ofsilica particles having an average size of 1.54 μm was added to thereaction system in Production Example 1, an ethylene glycol slurrycontaining 1 part of titanium oxide particles having an average size of0.27 μm was added to the reaction system in this example to obtainpolyester C. The content of titanium oxide in polyester C was 1% byweight.

PRODUCTION EXAMPLE 6 (POLYESTER FILM C1)

The same procedure as defined in Production Example 3 was conductedexcept that polyester A was replaced by polyester C to obtain 38 μmthick polyester film C1.

EXAMPLE 1

55 parts of methyl methacrylate as hydrophobic monomeric unit, 50 partsof an 80% aqueous solution of methacryloxyethyltrimethylammoniumchloride as cationic monomeric unit, 5 parts of one-endmethacryloxy-modified organopolysiloxane having a molecular weight ofapproximately 5,000 (FM0721 produced by Chisso Corp.) asorganopolysiloxane unit, 140 parts of ethyl alcohol and one part ofazobisisobutyronitrile as polymerization initiator were added and themixture was subjected to a 6-hour polymerization reaction at 80° C. in astream of nitrogen to obtain a 40% ethyl alcohol solution of a cationiccopolymer. This cationic copolymer was diluted with an ethylalcohol/isopropyl alcohol (50/50) mixed solvent, and the solution wasbar coated on one side of polyester film A1 so that the dry coatingthickness would become 0.2 μm, and then dried to form a coating layer.An acrylic adhesive was applied on the side opposite from the coatinglayer of the polyester film and protected with a release film to obtaina laminated film.

EXAMPLE 2

55 parts of methyl methacrylate as hydrophobic monomeric unit, 40 partsof an 80% aqueous solution of methacryloxyethyltrimethylammoniumchloride as cationic monomeric unit, 5 parts of a mercapto-modifiedorganopolysiloxane having a molecular weight of approximately 7,000(X-22-980 produced by Shin-Etsu Chemical Co., Ltd.) asorganopolysiloxane unit, 150 parts of isopropyl alcohol and one part ofazobisisobutyronitrile as polymerization initiator were added, and themixture was subjected to a 5-hour polymerization reaction at 80° C. in astream of nitrogen to obtain a 40% isopropyl alcohol solution of acationic copolymer. This cationic copolymer was diluted with isopropylalcohol and the solution was coated on one side of polyester film A1 sothat the dry coating thickness would become 0.15 μm, and then dried toform a coating layer. An acrylic adhesive was applied on the sideopposite from the coating layer and protected with a release film toobtain a laminated film.

EXAMPLE 3

51 parts of methyl methacrylate as hydrophobic monomeric unit, 50 partsof an 80% aqueous solution of methacryloxyethyltrimethylammoniumchloride as cationic monomeric unit, 4 parts of methacrylic acid, 140parts of ethyl alcohol and one part of azobisisobutyronitrile aspolymerization initiator were added, and the mixture was subjected to a6-hour polymerization reaction at 80° C. in a stream of nitrogen. Then 5parts of a both-end epoxy-modified organopolysiloxane having a molecularweight of approximately 1,000 (FM5511 produced by Chisso Corporation)was added as organopolysiloxane unit and the mixture was reacted at 80°C. for 10 hours to obtain a 40% ethyl alcohol solution of a cationiccopolymer. This cationic copolymer was diluted with ethyl alcohol andthe solution was bar coated on one side of polyester film A1 so that thedry coating thickness would become 0.2 μm, and then dried to form acoating layer. An acrylic adhesive was applied on the side opposite fromthe coating layer and protected with a release film to obtain alaminated film.

EXAMPLE 4

A mixture comprising 30 parts of an organopolysiloxane compound having astyrene group at one terminal and a number-average molecular weight of11,300 (X-22-2440 produced by Shin-Etsu Chemical Industries Co., Ltd.),70 parts of N,N-dimethylaminoethyl methacrylate and 150 parts ofisopropyl alcohol was heated, and when the temperature reached 80° C.and 2 hours thereafter, respectively, 0.3 parts ofazobisisobutyronitrile was added and the mixture was further reacted at80° C. for 8 hours to obtain a copolymer solution with 40% solids. Next,83.3 parts of isopropyl alcohol was added to the obtained copolymersolution, and then methyl chloride was introduced to the reactionsystem, allowing the mixture to react at 50° C. for 6 hours to obtain apolymer solution (4A) having organopolysiloxane units and quaternaryammonium salt units with a solids concentration of 34%.

Then, 163 parts of a mixture of 67 mol % of dipentaerythritolpentaacrylate and dipentaerythritol hexaacrylate (Kayarad DPHA producedby Nippon Kayaku Co., Ltd.), 21.8 parts of pyromellitic aciddianhydride, 100 parts of methyl ethyl ketone, 0.1 part of hydroquinonemonomethyl ether and one part of N,N-dimethylbenzylamine were added andreacted at 80° C. for 8 hours to obtain a carboxyl group-containingpolyfunctional acrylate solution (4B) with a solids concentration of65%.

17 parts of (4A) obtained above, 83 parts of (4B), 3 parts of Ilgacure907 (produced by Ciba Speciality Chemicals Co., Ltd.) asphotopolymerization initiator and 897 parts of isopropyl alcohol weremixed uniformly to prepare an active energy ray-curing coatingcomposition. Then, this composition was coated on one surface ofpolyester film A1 so that the coating thickness after curing wouldbecome 0.15 μm, and the coating was irradiated by a 120 W/cm energy highpressure mercury arc lamp from a distance of 100 mm for 15 seconds toform a coating layer. An acrylic adhesive was applied on the sideopposite from the coating layer of the film A1 and protected with arelease film to obtain a laminated film.

EXAMPLE 5

A mixture comprising 10 parts of an organopolysiloxane compound havingmercapto groups at both terminals and a number-average molecular weightof approximately 3,340 (X-22-167B produced by Shin-Etsu Chemical Co.,Ltd.), 80 parts of N,N-dimethylaminoethyl methacrylate, 10 parts ofmethyl methacrylate and 150 parts of isopropyl alcohol was heated, andwhen the temperature reached 80° C. and 2 hours thereafter,respectively, 0.3 parts of azobisisobutyronitrile was added, and themixture was reacted at 80° C. for 8 hours to obtain a copolymer solutionwith 40% solids. Next, 83.3 parts of isopropyl alcohol was added to theobtained copolymer solution, and then methyl chloride was introduced tothe reaction system, allowing the mixture to react at 50° C. for 6 hoursto obtain a 35% solids concentration polymer solution (5A) havingorganopolysiloxane units and quaternary ammonium salt units.

17 parts of (5A) obtained above, 53 parts of dipentaerythritolhexaacrylate, 3 parts of Ilgacure 907 (produced by Ciba SpecialityChemicals Co., Ltd.) as photopolymerization initiator and 927 parts ofisopropyl alcohol were mixed uniformly to prepare an active energyray-curing coating composition. Then, this composition was coated on onesurface of polyester film A1 so that the coating thickness after curingwould become 0.15 μm, and irradiated by a 120 W/cm energy high pressuremercury arc lamp from a distance of 100 mm for 15 seconds to form acoating layer. An acrylic adhesive was applied on the side opposite fromthe coating layer of the film A1 and protected with a release film toobtain a laminated film.

EXAMPLE 6

A mixture comprising 15 parts of an organopolysiloxane compound having amethacryloyl group at one terminal and a number-average molecular weightof approximately 10,000 (FM0725 produced by Chisso Corp.), 75 parts ofN,N-dimethylaminoethyl methacrylate, 10 parts of 2-hydroxyethylmethacrylate and 150 parts of methyl ethyl ketone was heated, and whenthe temperature reached 80° C. and 2 hours thereafter, respectively, 0.3parts of azobisisobutyronitrile was added, and the mixture was reactedat 80° C. for 8 hours to obtain a copolymer solution with 40% solids. Tothis solution, 8 parts of methacryloyl isocyanate was added, and themixture was reacted at 80° C. for 6 hours to obtain a copolymer solutionwith 42% solids having a methacryloyl group in the side chain. Next, 300parts of isopropyl alcohol was added to the obtained copolymer solution,and then methyl chloride was introduced to the reaction system to carryout reaction at 50° C. for 6 hours to obtain a polymer solution (6A)with a 22% solids concentration having organopolysiloxane units andquaternary ammonium salt units and also containing methacryloyl groups.

26 parts of (6A) obtained above, 53 parts of dipentaerythritolhexaacrylate, 3 parts of Ilgacure 907 (produced by Ciba SpecialityChemicals Co., Ltd.) as photopolymerization initiator and 918 parts ofisopropyl alcohol were mixed uniformly to prepare an active energyray-curing coating composition. Then, this composition was coated on onesurface of polyester film A1 so that coating thickness after curingwould become 0.15 μm, and irradiated by a 120 W/cm energy high pressuremercury arc lamp from a distance of 100 mm for 15 seconds to form acoating layer. An acrylic adhesive was applied on the side opposite fromthe coating layer and protected with a release film to obtain alaminated film.

EXAMPLE 7

A mixture comprising 10 parts of an organopolysiloxane compound having astyrene group at one terminal and a number-average molecular weight of11,300 (X-22-2440 produced by Shin-Etsu Chemical Co., Ltd.), 80 parts ofN,N-dimethylaminoethyl methacrylate, 10 parts of 2-hydroxyethylmethacrylate and 150 parts of methyl ethyl ketone was heated, and whenthe temperature reached 80° C. and 2 hours thereafter, respectively, 0.3parts of azobisisobutyronitrile was added, allowing the mixture to reactat 80° C. for 8 hours to obtain a copolymer solution with 40% solids. Tothis solution was added 50 parts of a compound obtained by reacting 28parts of isophorone diisocyanate and 22 parts of 2-hydroxyethylacrylate, and the mixture was reacted at 80° C. for 6 hours to obtain acopolymer solution with 50% solids having an acryloyl group in the sidechain.

Next, 300 parts of isopropyl alcohol was added to the copolymer solutionobtained here, and then methyl chloride was introduced to the reactionsystem to carry out reaction at 50° C. for 6 hours to obtain a polymersolution (7A) with 28% solids concentration having organopolysiloxaneunits and quaternary ammonium salt units and also having an acryloylgroup in the side chain.

20 parts of (7A) obtained above, 53 parts of dipentaerythritolhexaacrylate, 6 parts of Darocure 1173 produced by Ciba SpecialtyChemicals Co., Ltd., as photopolymerization initiator, and 921 parts ofisopropyl alcohol were mixed uniformly to prepare an active energyray-curing coating composition. Then, this composition was coated on onesurface of polyester film A1 so that coating thickness after curingwould become 0.15 μm, and irradiated by a 120 W/cm energy high pressuremercury arc lamp from a distance of 100 mm for 15 seconds to form acoating layer. An acrylic adhesive was applied on the side opposite fromthe coating layer and protected with a release film to obtain alaminated film.

EXAMPLE 8

17 parts of the polymer solution (4A) obtained in Example 4, 53 parts ofdipentaerythritol hexaacrylate, 6 parts of Ilgacure 184 (produced byCiba Specialty Chemicals Co., Ltd.) as photopolymerization initiator,and 924 parts of isopropyl alcohol were mixed uniformly to prepare anactive energy ray-curing coating composition. Then, this composition wascoated on one surface of the polyester film Al so that coating thicknessafter curing would become 0.15 μm, and irradiated by a 120 W/cm energyhigh pressure mercury arc lamp from a distance of 100 mm for 15 secondsto form a coating layer. An acrylic adhesive was applied on the sideopposite from the coating layer of the polyester film and protected witha release film to obtain a laminated film.

COMPARATIVE EXAMPLE 1

Sodium p-styrenesulfonate (40 parts), sodium vinylsulfonate (40 parts)and N,N′-dimethylaminomethacrylate (20 parts) were dissolved indistilled water, to which 2,2′-azobis(2-aminodipropane)dihydrochloridewas added as polymerization initiator with stirring under heating at 60°C to carry out polymerization, thereby obtaining an antistatic resin.Then, to 30 parts of this antistatic resin were blended 50 parts of apolyurethane resin (a polyester polyol comprising isophoronediisocyanate as isocyanate component, and terephthalic acid, isophthalicacid, ethylene glycol or diethylene glycol as polyol component;chain-lengthening agent: 2,2-dimethylolpropionic acid), 10 parts of anacrylic resin (comprising the following units: methyl methacrylate,N,N′-dimethylaminoethyl methacrylate, 2-hydroxyethyl methacrylate andbutyl acrylate), 5 parts of a trifunctional water-soluble epoxy compoundand 5 parts of colloidal silica having an average particle size of 0.1μm to prepare a water-dispersed coating solution.

Then the same procedure as defined in Production Example 4 was conductedexcept that after stretching the sheet in the machine direction, thesaid water-dispersed coating solution was coated so that coatingthickness after stretching and drying would become 0.1 μm to obtainpolyester film B2. An acrylic adhesive was applied on the side oppositefrom the water-dispersed coating layer of the said polyester film B2 andprotected with a release film to obtain a laminated film.

COMPARATIVE EXAMPLE 2

60 parts of methyl methacrylate as hydrophobic monomeric unit, 50 partsof an 80% aqueous solution of methacryloxyethyltrimethylammoniumchloride as cationic monomeric unit, 140 parts of ethyl alcohol and onepart of azobisisobutyronitrile as polymerization initiator were addedand subjected to a 6-hour polymerization reaction at 80° C. in a streamof nitrogen to obtain a 40% ethyl alcohol solution of a cationiccopolymer. This cationic copolymer was diluted with an ethylalcohol/isopropyl alcohol (50/50) mixed solvent, bar coated on one sideof polyester film B1 so that dry coating thickness would become 0.2 μm,and dried to form a coating layer. An acrylic adhesive was applied onthe side opposite from the coating layer and protected with a releasefilm to obtain a laminated film.

COMPARATIVE EXAMPLE 3

A mixture comprising 80 parts of N,N-dimethylaminoethyl methacrylate, 20parts of methyl methacrylate and 150 parts of isopropyl alcohol washeated, and when the temperature reached 80° C. and 2 hours thereafter,respectively, 0.3 parts of azobisisobutyronitrile was added, and themixture was reacted at 80° C. for 8 hours to obtain a copolymer solutionwith 40% solids. Next, 83.3 parts of isopropyl alcohol was added to thethus obtained copolymer solution, and then methyl chloride wasintroduced to the reaction system to carry out reaction at 500° C. for 6hours to obtain a polymer solution (8A) having quaternary ammonium saltunits with a solids concentration of 34%.

17 parts of (8A) obtained above, 53 parts of dipentaerythritolhexaacrylate, 3 parts of Ilgacure 907 (produced by Ciba SpecialtyChemicals Co., Ltd.) as photopolymerization initiator and 927 parts ofisopropyl alcohol were mixed uniformly to prepare an active energyray-curing coating composition. Then, this composition was coated on onesurface of polyester film B1 so that coating thickness after curingwould become 0.15 μm, and irradiated by a 120 W/cm energy high pressuremercury arc lamp from a distance of 100 mm for 15 seconds to form acoating layer. An acrylic adhesive was applied on the side opposite fromthe coating layer and protected with a release film to obtain alaminated film.

COMPARATIVE EXAMPLE 4

A laminated film was obtained in the same way as in Example 1 exceptthat the dry coating thickness was altered to 0.1 μm.

COMPARATIVE EXAMPLE 5

A laminated film was obtained in the same way as in Example 4 exceptthat polyester film A1 was replaced by polyester film C1.

The properties of the thus obtained laminated films of Examples 1 to 8and Comparative Examples 1 to 5 are shown in Tables 1 and 2 given below.TABLE 1 Example 1 Example 2 Example 3 Example 4 Surface resistance 3 ×10⁹ 3 × 10⁹ 1 × 10⁹ 9 × 10⁸ P2 (mN/cm) 2100 2200 2100 2200 P1 (mN/cm)2400 2500 2400 2500 P1 − P2 (mN/cm) 300 300 300 300 Total lighttransmittance 90 90 90 90 Haze 0.9 0.9 0.9 0.9 Adhesion of dusts NoneNone None None Adhesion of adhesives None None None None Clarity A A A AExample 5 Example 6 Example 7 Example 8 Surface resistance 5 × 10⁸ 7 ×10⁸ 5 × 10⁸ 4 × 10⁸ P2 (mN/cm) 2200 2200 2200 2200 P1 (mN/cm) 2500 25002500 2500 P1 − P2 (mN/cm) 300 300 300 300 Total light transmittance 9090 90 90 Haze 0.9 0.9 0.9 0.9 Adhesion of dusts None None None NoneAdhesion of adhesives None None None None Clarity A A A A

TABLE 2 Comparative Example 1 2 3 4 5 Surface 6 × 10⁸ 1 × 10⁹ 3 × 10¹¹ 1× 10⁹ 9 × 10⁸ resistance P2 (mN/cm) 4000 3100 2200 2260 2200 P1 (mN/cm)4300 3400 2500 2290 2500 P1 − P2 (mN/cm) 300 300 300 300 300 Total light88 89 90 90 75 transmittance Haze 3.7 3.4 0.9 1.0 15 Adhesion of NoneNone Present None None dusts Adhesion of Present Present None None Noneadhesives Clarity A A A A A

INDUSTRIAL APPLICABILITY

The film of the present invention excels in transparency, antistaticproperties, chemical resistance, scratch resistance, handling quality,etc., and consequently it can facilitate the tests of high-precisionliquid crystal display boards, etc. It also has the characteristicproperties such as being excellent in preventing adhesion or depositionof adhesives, dusts, etc., on the liquid crystal display boards.Further, when the film is separated and discarded as useless matterafter performing the role of protecting the polarizing plate, suchseparation can be effected with ease, producing an effect of inhibitingseparation charging, thus making it possible to provide a base for thepolarizing plate protective films which is capable of preventing damageto the circuits connected to the liquid crystal display board due tosuch separation charging, so that the industrial value of the presentinvention is high.

1. A base for polarizing plate protective film, which base is stuck onthe surface of a polarizing plate of a liquid crystal display board,comprises a biaxially oriented polyester film having a coating layer onone surface thereof and has such properties that: the surface resistanceof said coating layer is not higher than 1×10¹¹ Ω, the adhesive force(P2) of the acrylic adhesives to the coating layer surface is not morethan 3,000 mN/cm, the difference (P1-P2) between the adhesive force (P1)of the rubber adhesives to the coating layer surface and the adhesiveforce (P2) of the acrylic adhesives is not less than 100 mN/cm and thefilm haze is not higher than 2%.
 2. A base for polarizing plateprotective film according to claim 1, wherein the coating layer containsan antistatic agent.
 3. A base for polarizing plate protective filmaccording to claim 1, wherein the coating layer contains siliconecompound.
 4. A base for polarizing plate protective film according toclaim 1 wherein thickness of the coating layer is 0.01 to 0.3 μm.
 5. Abase for polarizing plate protective film according to any one of claims1 to 4, wherein the polyester film has an adhesive layer on the sideopposite from the coating layer.
 6. A base for polarizing plateprotective film according to claim 5 wherein the adhesive layercomprises at least one type of adhesive selected from the groupconsisting of acrylic adhesive, rubber adhesive, block copolymeradhesive, polyisobutyrene adhesive and silicone adhesive.
 7. A base forpolarizing plate protective film according to claim 5 wherein a releasefilm is laminated on the adhesive layer surface.
 8. A base forpolarizing plate protective film according to claim 6 wherein a releasefilm is laminated on the adhesive layer surface.
 9. A base forpolarizing plate protective film according to claim 2, wherein thecoating layer contains silicone compound.
 10. A base for polarizingplate protective film according to claim 2 wherein thickness of thecoating layer is 0.01 to 0.3 μm.
 11. A base for polarizing plateprotective film according to claim 3 wherein thickness of the coatinglayer is 0.01 to 0.3 μm.
 12. A base for polarizing plate protective filmaccording to claim 9 wherein thickness of the coating layer is 0.01 to0.3 μm.
 13. A base for polarizing plate protective film according to anyone of claims 9-12, wherein the polyester film has an adhesive layer onthe side opposite from the coating layer.
 14. A base for polarizingplate protective film according to claim 13 wherein the adhesive layercomprises at least one type of adhesive selected from the groupconsisting of acrylic adhesive, rubber adhesive, block copolymeradhesive, polyisobutyrene adhesive and silicone adhesive.
 15. A base forpolarizing plate protective film according to claim 13 wherein a releasefilm is laminated on the adhesive layer surface.
 16. A base forpolarizing plate protective film according to claim 14 wherein a releasefilm is laminated on the adhesive layer surface.